The present invention relates to a satellite broadcasting receiver, particularly to an antenna arrangement comprising a frequency down converter for converting an electromagnetic wave received by a parabolic antenna to a signal having a lower frequency.
A satellite broadcasting receiver is used for receiving an electromagnetic wave transmitted by a satellite positioned on a stationary orbit in the sky, and generally comprises a parabolic antenna, a waveguide situated at a focus of the parabolic antenna, a frequency down converter having a strip line, and a mode converter provided between the waveguide and the strip line of the freqeuncy down converter for converting a waveguide mode (TE.sub.01 mode) to a strip line mode (TEM mode). An output of the frequency converter is applied to a domestic television receiver through a FM-AM converter or a demodulator.
In a conventional satellite broadcasting receiver, the electromagnetic wave is guided to the outside of the parabolic antenna though the waveguide where the mode converter and the frequency down converter are provided, or the waveguide, the mode converter and the frequency down converter are unified in one body and provided at the focus of the parabolic antenna. However, in this conventional receiver, the mode conversion is processed sequentially from the waveguide mode to the strip line mode through the coaxial cable mode, and the configuration becomes excessively complex. On the other hand, a mode converter for directly converting the rectangular waveguide mode to the strip line mode is also employed. However, in a situation where a mode converter of this kind is employed, two waves of different polarizations cannot be received without the rotation of the whole antenna. Moreover, when the receiver is arranged for simultaneously receiving these two kinds of differently polarized waves, it is necessary that these two kinds of polarized waves should be derived respectively from different positions of the waveguide provided at the focus of the parabolic antenna, resulting in the additional disadvantage that the effective area of the parabolic antenna is reduced.